1980s: Mount Saint Helens volcano erupts, causing loss of life and sending up thick black clouds of ash that darken the skies in the Pacific Northwest. This is the largest volcanic explosion ever in the United States.

Today: A tidal wave sweeps over wide-ranging coastlines from Indonesia to Africa, killing hundreds of thousands of people. The earthquake that sets off the tsunami is so strong that it causes the earth to wobble on its axis and permanently shifts various geographical formations, including islands off the coast of Sumatra.

1980s: The spacecraft Columbia makes its first trip into space in 1981. Five years later the space shuttle Challenger explodes on liftoff from the Kennedy Space Center. Seven astronauts die.

Today: The Columbia explodes before its scheduled landing in Florida. Seven crew members are killed.